Effects Of Drought Stress On Endogenous Hormones,Growth And Fruit Quality Of Sweet Pepper

Taking Catherine as test materials,the experiment with four soil moisture contents(field water holding capacity of 60%-70%,50%-60%and 40%-50%was light stress LS,moderate stress MS and severe stress SS,with field water holding capacity of 70%-80%as normal irrigation CK)was conducted to systematically study the effect of different drought stress on changes in endogenous hormones in terminal buds,the plant growth dynamics,external quality and nutritional dynamics of the fruit and the yield in sweet pepper plants.The results of the study are as follows:(1)Drought stress inhibited the secretion of IAA and ZT content,but promoted the secretion of ABA content.The more severe the drought stress,the lower levels of IAA/ZT,IAA/GA3 and(IAA+GA3)/ABA in the terminal buds of sweet pepper.There was no significant different on ABA and GA3 content between LS and CK throughout the observation period.However,the level of IAA/GA3 in LS showed an increasing trend in the middle and late period of drought stress.(2)Drought stress significantly inhibited plant height,stem diameter,leaf area and the dry mass of stem and leaf,but LS promoted accumulation of the root dry mass during the late growth period.The maximum values of leaf growth rate and relative expansion rate decreased with the increasing level of drought stress.With the extension of stress time,the leaf growth rate and relative expansion rate in LS and MS were higher than in CK during the late growth period.The drought stress forced the beginning point,peak point and end point of plant height and stem diameter,and shortened the rapid growth time of plant height and stem diameter.The beginning point,peak point and end point of leaf were delayed in LS and MS;drought stress prolonged the leaf rapid growth time in sweet pepper.(3)Drought stress decreased fruit equatorial diameter,fruit longitudinal diameter,the maximum values of fruit equatorial and longitudinal diameter growth rate,and prolonged the rapid growth time of fruit equatorial and longitudinal diameter.With the extension of stress time,fruit equatorial diameter and fruit longitudinal diameter in LS were higher than in CK in the middle and late growth period.The beginning point and end point of fruit equatorial diameter growth rate and fruit longitudinal diameter growth rate were advanced in MS and SS but delayed in LS.Morever,LS had no effect on fruit dry mass.(4)The fruit weight of sweet pepper was significantly reduced under drought stress.MS and SS decreased the fruit number and yield per plant,inhibited the increase of Vc,soluble protein,organic acid and anthocyanin contents of fruit,promoted the accumulation of soluble sugar and free amino acid.However,LS increased the contents of Vc,anthocyanin and the fuit number,but did not change the soluble protein content,free amino acid content,peel thickness,shape index in fruit and yield per plant.(5)CA analysis revealed that,drought stress affected the secretion of endogenous hormones,plant growth,dry matter accumulation,and fruit nutrient composition.The effect of drought stress on fruit nutrition indexes was mainly reflected in the middle and late growth stages of fruit.Above all,proper drought stress,especially LS,might change the IAA/GA3 levels,stimulate the later development of roots,promote the growth leaves and fruits in the later growth period of sweet pepper,and increase fruit Vc,anthocyanin contents and the fruit number per plant without influncing the yield.While excessive drought stress was not conducive to plant growth and dry matter accumulation of sweet pepper,and reduce the fruit quality and yield.